1. Field of the Invention
The invention relates to a method of producing a piston for an internal combustion engine including at least one strengthened piston ring groove.
It is especially where highly loaded pistons are concerned in both diesel and petrol engines that the load on the topmost piston ring groove is particularly high. This is why this piston ring groove needs to be specially strengthened by special hard-wearing materials.
2. Prior Art
It is known from EP 0 654 596 A1 to include a ring of an iron based alloy in casting a piston body and to then work out the piston ring groove from this ring.
As an alternative, it is known to work out the groove from the material of the piston skirt and to render the flanks of the groove with good hard-wearing properties in a suitable subsequent process, by hard anodizing for example. In this case, however, high costs materialize from disposal of the ferrous alfin and waste chemicals as well as from the working processes involved.
Known from DE 198 33 827 C1 is to configure the strengthening of cermaic material in the region of the groove flanks which is likewise relatively complicated, however.
DE 34 05 983 C1 describes hardfacing the flanks of the piston ring grooves with austentic hard manganese steel. Such a method, however, exposes the piston to relatively high thermal stress. Furthermore, this requires a relatively large amount of strengthening or filler materials.
The invention is based on the objective of providing a method with which a piston for an internal combustion engine, requiring to comprise at least one strengthened piston ring groove, can now be produced at little expense.
The achievement of this objective reads from the method as described in claim 1.
In accordance therewith, a strengthened piston ring groove is configured on a piston for an internal combustion engine by configuring at least one, preferably two, relatively narrow grooves in the region of the upper and/or lower flank of the piston ring groove provided. More particularly, these grooves may be incised. Between the two grooves, or in the vicinity of the one groove, a web of the base material remains which, as described in the following, needs to be removed.
After the groove(s) have been configured, at the locations at which the upper and/or lower flanks of the piston ring groove is provided, these groove(s) are filled with a hard-wearing material preferably by means of a single-stage coating procedure. In conclusion, the piston ring groove is worked out of the piston such that the upper and/or lower flank of the piston ring groove is formed by the hard-wearing material. In other words, in the course of the last step, the web of base material remaining between the relatively narrow grooves as well as part of each filling of hard-wearing material are removed. Part of the filling, consisting of the hard-wearing material, remains at the upper and/or lower flank of the piston ring groove configured in this way, so that the at least one flank of the groove consists of a material, with the aid of which, the requirements on the flanks of the piston ring groove are satisfied.
The method in accordance with the invention offers the advantage of the piston being exposed to less thermal stress than is the case in known hardfacing. Furthermore, since only relatively narrow grooves are filled with the strengthening or filler material, less material is used. Due to the reduced filler volume less time is needed for processing. As compared to casting a ring of hard-wearing material in place in a base body of the base material and subsequently working out the groove from the cast-in place ring, the material requirement is likewise less. In conclusion, the consumption of strengthening material, processing time and other process parameters remain the same, irrespective of how the geometry and width of the ring groove is configured. In other words, the locations at which the relatively narrow grooves are configured, as well as their geometry and the geometry of the subsequently worked-out piston ring groove can now be freely selected without the method in accordance with the invention requiring any appreciable change or complication.
Preferably further embodiments of the invention are described in the further claims.
It is good practice to implement the step of filling the relatively narrow groove(s) configured in the base body by means of a laser or plasma source. By these steps in processing, advantageous filling of hard-wearing material is achievable at low expense.
Tests have furthermore indicated it to be of advantage to use microspraying for filling the groove(s).
In conclusion, use is made preferably of a wire- or powder-type material for the filling step. Such materials permit particularly good handling so that in this case a particularly simple variant of the method in accordance with the invention is achieved.